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Describing sets of characters (csets) in Icon

Before we look at Icon's functions for analyzing strings, we must first understand the idea of the cset, which is a basic Icon type that describes sets of characters.

Csets are for describing generic types of characters, such as ``letters,'' ``digits,'' and ``punctuation marks.'' Mathematically, a cset is a subset of the external character set (such as ASCII).

For example, suppose we want to talk about ``delimiter'' characters, where a delimiter is either a period, comma, or slash. This Icon statement would define a variable called delim as this cset:

    delim  :=  '.,/';

• ``&digits'' is the cset of digits from 1 to 9.
• ``&letters'' is the cset of all letters, both uppercase and lowercase.
• ``&lcase'' is the cset of lowercase letters, and ``&ucase'' is the cset of uppercase letters.